The standard method for analysis of volatile organic compounds in water has been purge and trap, in which a water sample, typically 40 ml, is purged with a gas stream for a period of time and the volatile organic compounds which are partitioned into the gas stream are then trapped on a sorbent cartridge and analyzed by thermal desorption gas chromatograph/mass spectrometer. This means that grab samples had to be acquired and analyzed from water wells, surface water, process streams, etc. If a treatment process had to be characterized over a period of time, only a finite number of samples could be acquired for this purpose. Two spray and trap methods for water analysis utilizing a spray nozzle that volatilized aqueous organics for adsorption on a trap prior to analysis were discussed in recent publications. (Gerhard Matz and Peter Kesners, "Spray and Trap Method for Water Analysis by Thermal Desorption Gas Chromatography/Mass Spectrometry in Field Applications", Anal. Chem., 1993, 65, 2366-2371 and Gokkhan Baykut and Annette Voigt, "Spray Extradion of Volatile Organic Compounds from Aqueous Systems into the Gas Phase for Gas Chromatography/Mass Spectrometry", Anal. Chem. 1992, 64, 677-681). Another publication discussed an on line monitoring of volatiles in aqueous solutions using membrane introduction mass spectrometry. (Scott J. Bauer and R. Graham Cooks, "MIMS for trace-level determination of organic analytes in on-line process monitoring and environmental analysis", American Laboratory, October 1993, pp. 36, 38-43, 45-48, 51, 52). However, the membrane introduction mass spectrometry is not applicable to larger or more polar compounds.
U.S. Pat. No. 5,272,337 to Thompson et al. describes a mass spectrometer sample introduction system for introducing gaseous samples from a wide range of environmental matrices into a mass spectrometer for analysis of the samples. A water purge sample module uses a vial containing water containing volatile compounds and a high speed needle sparge purging system for extracting the volatile compounds from the water for analysis in the mass spectrometer. This method requires obtaining separate samples in a vial and analyzing the volatile compounds extracted from the water one at a time.
Other methods such as IR have been used but are not as sensitive or specific in their identification of compounds of interest. The present invention fulfills the need for a continuous analysis in real-time of volatile organic compounds in water samples or process streams with detection limits in the low ppb range.